docs: def p_jsonpath_named_operator(self, p):
          "jsonpath : NAMED_OPERATOR"
          if p[1] == 'len':
              p[0] = _iterable.Len()
          elif p[1] == 'sorted':
              p[0] = _iterable.SortedThis()
          elif p[1].startswith("split("):
              p[0] = _string.Split(p[1])
          elif p[1].startswith("sub("):
              p[0] = _string.Sub(p[1])
          else:
              super(ExtentedJsonPathParser, self).p_jsonpath_named_operator(p)